This application is based on Japanese Patent Application No. 2001-104999 filed on Apr. 3, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a leak check apparatus for a fuel vapor purge system. The apparatus detects a leak on a fuel vapor purge system including a fuel tank.
2. Description of Related Art
In a Conventional fuel vapor purge system, a canister communicates with a fuel tank via a gas line that introduces an evaporated fuel vapor (referred to as a vapor) from the fuel tank to the canister. The vapor is adsorbed in the canister. The canister also communicates with the atmosphere via an intake line with a canister close valve (referred to as a canister valve). The canister also communicates with an intake passage via a purge-line with a purge control valve (referred to as a purge valve). Further, a controller is provided for operating the valves to adsorb the vapor in the canister and to desorb an adsorbed vapor into the intake passage. The controller also operates the valves to detect a leak on the system including the fuel tank and pipes providing the lines. The controller opens the purge-valve and closes the canister valve when an engine runs and an intake pressure is a negative pressure. Then, the controller closes the purge-valve when an inside pressure in the fuel tank reaches to a predetermined negative pressure. The controller monitors the inside pressure and detects the leak based on a variation of the inside pressure or an elapsed time until the inside pressure decreases to a specific pressure.
However, in the conventional system, since the leak check procedure is executed during the engine is running, unstable fuel level that may wave due to a vibration of the engine or a vehicle affect a leak check accuracy. Further, since the negative pressure should be introduced into the system in a short period of time, the engine may supply an excessive amount of vapor that may make an exhaust emission worse.
It is an object of the present invention to reduce an emission during a leak check procedure is executed.
It is another object of the present invention to improve an accuracy of a leak check of a fuel vapor purge system.
According to a first aspect of the present invention, an apparatus includes at least one valve which defines a closed space including a fuel tank, a main canister and at least a part of a purge passage. This closed space is subject to a leak check. A pump is disposed for discharging gaseous component in the closed space and for reducing an inside pressure of the closed space. A sub canister disposed in series to the pump which adsorb the vapor in the gaseous component discharged by the pump. Therefore, an emission of the vapor is reduced. A sensor is disposed for outputting a signal indicative of a leak on the closed space. Therefore, it is possible to detect the leak on the closed space with no significant increase of emission of the vapor.
The leak check procedure executed by using the components of the apparatus may be executed when the engine is stopped. According to this arrangement, it is possible to improve accuracy of the leak check.
According to another aspect of the present invention, an apparatus has at least one valve which defines a closed space including the fuel tank, the main canister and at least a part of the purge passage, and connects at least the remaining part of the purge passage to the intake passage of the engine. A pump is disposed on the system for pressurizing the closed space when the engine is stopped. A first sensor is disposed on the system for outputting a signal indicative of a leak on the closed space. Therefore, it is possible to detect the leak on the closed space while the engine is stopped. The apparatus further comprises a second sensor disposed on the engine which outputs a signal indicative of a leak on the remaining part of the purge passage when the engine is running. Since the remaining part of the purge passage is connected to the intake passage of the engine by the valve, a condition of the engine is influenced by the leak, and the sensor detects the condition. Therefore, it is possible to detect the leak on the remaining part. Further, a fluctuation caused by a wave on the fuel level does not affect on the leak check for the remaining part since the fuel tank is subject to the leak check while the engine is stopped.